John M. Krochta

Summary: Four % (wt/wt) aqueous solutions were prepared at corn starch:methylcellulose:whey protein isolate (CS:MC:WPI) ratios of 2:2:2, 1:2:3, 2:1:3, 2:2:0, 1:2:0 and 2:1:0. Glycerol (gly) was used as a plasticiser at CS–MC–WPI:gly ratios of 2:1, 2.5:1 and 3:1. CS–MC–WPI blend films were stronger than CS–WPI films and had lower oxygen permeability (OP) than MC–WPI films. The highest tensile strength (TS) of blend films was 8.01 ± 3.41 MPa, at CS:MC:WPI ratio of 2:2:0 and CS–MC–WPI:gly ratio of 3:1. Lowest OP value was 45.05 ± 7.24 cm³ μm m⁻² per day kPa⁻¹, at CS:MC:WPI ratio of 2:2:2 and CS–MC–WPI:gly ratio of 3:1. OP values were predictable based on relative amounts of components. However, TS and elastic modulus properties of the CS–MC–WPI blend films did not reflect the relative amounts of the components. All of CS–MC–WPI films were translucent indicating some degree of immiscibility among the CS, MC and WPI. These results indicate the influence of complex molecular interactions among the components.

Whey protein concentrate (WPC) was explored alone and in combination with sucrose (Suc) plasticizer as a grease‐barrier coating for bulrush pulpboard and solid bleached sulfate paperboard used in food packaging. WPC‐coated and WPC : Suc‐coated pulpboards showed better oil‐barrier properties compared with untreated, water‐treated or Suc‐coated pulpboards. Coating formulations with 10% WPC, without and with Suc, resulted in oil barriers comparable with commercial fluorinated hydrocarbon for pulpboard. When pulpboard trays containing cheesy pasta were microwave‐heated, 10% WPC : 20% Suc solution‐coated trays showed grease barrier property comparable with fluorinated hydrocarbon‐treated trays. Caramelization and Maillard browning of WPC and WPC : Suc coatings were initiated at 300°F, but microwave‐heated foods do not normally reach this high temperature. Paperboard with 10% WPC : 20% Suc solution coating had oil barrier comparable with polyethylene‐coated paperboards. WPC : Suc solution mixture at 2.5% : 5% and 3.3% : 7% were determined as the solution concentration minima for 4 and 24 h tests, respectively. HunterLab colorimeter L and b values indicated slight colour change of the paperboard coated with the higher WPC concentration solutions. Coating resulted in thicker paperboards but not in a linear manner. The 10% WPC : 20% Suc solution‐coated solid bleached sulfate paperboards on which slabs of butter sat in a refrigerator did not show any butterfat penetration, comparable with polyethylene‐coated paperboards and unlike uncoated paperboards that showed poor butterfat‐barrier properties. WPC : Suc coating was shown in this study to have potential to replace synthetic materials as a grease barrier. Copyright © 2011 John Wiley & Sons, Ltd.

Abstract:  Residual O ₂ in a package headspace can be removed by an O ₂ ‐absorbing sachet, which can be harmful if swallowed by the consumer, or by a chemically‐active plastic packaging film, which is difficult to recycle. An edible, O ₂ ‐absorbing film would avoid these disadvantages. The objective of our research was to assess the O ₂ ‐scavenging potential of an edible whey protein isolate (WPI) film incorporating ascorbic acid (AA). AA at 0.05, 0.1, or 0.2 M was added to 5% (w/w) heat‐denatured WPI film‐forming solutions with WPI : glycerol (Gly) ratio of 1 : 1.00, 1 : 0.80, or 1 : 0.67. The pH of solutions was then adjusted to 3.5 (below pK _a1 of AA), to stabilize AA against oxidation, before film casting. The mechanical properties, O ₂ permeabilities, and thermal transitions of films were measured. Activation of the O ₂ ‐scavenging function of the AA‐incorporated films was accomplished by adjustment of the films to pH ≥ 7. O ₂ ‐scavenging ability of AA‐incorporated WPI films was determined by measuring residual O ₂ in the headspace of a high‐barrier container. Incorporation of AA into WPI film decreased film tensile strength and further reduced O ₂ permeability at each WPI : Gly ratio. AA‐containing films adjusted to pH ≥ 7 demonstrated O ₂ absorption proportional to AA content, consistent with theoretical O ₂ ‐scavenging capacity. Thermal transition measurements indicated that AA was involved in WPI structural modification and decreased the degradation temperature of WPI‐based film. The demonstrated O ₂ ‐scavenging function, improved O ₂ barrier and acceptable mechanical properties of AA‐incorporated films indicate potential commercial usefulness. Practical Application:  Ascorbic acid‐incorporated whey protein film with oxygen scavenging function can be used to extend shelf lives of a wide variety of oxygen‐sensitive products by eliminating headspace oxygen as well as oxygen permeating through the packaging wall over time. Edible oxygen‐scavenger film has the advantages of avoiding both accidental consumption and nonrecyclability of conventional oxygen scavenger systems.

BACKGROUND: Films made from different protein (P) or polysaccharide (PS) materials have widely different properties. The objective of this study was to determine whether whey protein isolate (WPI)‐PS blended films possess a combination of properties intermediate and possibly superior to WPI or PS film alone.RESULTS: Oxygen permeability (OP) and tensile strength (TS) for PS‐WPI blended films were intermediate between the OP and TS properties of pure methycellulose (MC), hydroxypropylmethylcellulose (HPMC) or sodium alginate (SA) film and pure WPI film. Starch‐WPI blends gave the weakest films. Water vapor permeability values for all pure and blended films were similar. Blended films made of MC, HPMC or SA with WPI had lower transparency than pure MC, HPMC, SA or WPI films. Differential scanning calorimetry thermograms obtained from the blended films exhibited a single glass transition temperature (T_g) at an intermediate value between the T_g values of the pure films.CONCLUSIONS: Whether properties of PS‐WPI blended films are intermediate to properties of the pure PS and WPI film depends on the particular PS and specific property. In the case of MC or HPMC with WPI, the blended films reflect the higher TS of the PS and lower OP of the WPI. Copyright © 2011 Society of Chemical Industry

ABSTRACT:  This study investigated the use of whey protein, as an additional coating, in combination with basic, well‐described predust, batter, and breading ingredients, for fat‐uptake reduction in fried chicken. Chicken breasts were cut into strips (1 × 5 × 10 cm) and coated with wheat flour (WF) as a predust, dipped in batter, coated with WF as a breading, then dipped in 10% denatured whey protein isolate (DWPI) aqueous solution (wet basis). A WF‐batter‐WF treatment with no DWPI solution dip was included as a control. Coated chicken strips were deep‐fried at 160 °C for 5 min. A Soxhlet‐type extraction was performed to determine the fat content of the meat fraction of fried samples, the coating fraction of fried samples, raw chicken, and raw coating ingredients. The WF‐batter‐WF‐10% DWPI solution had significantly lower fat uptake than the WF‐batter‐WF control, by 30.67% (dry basis). Practical Application: This article describes applied research involving fat reduction in coated deep‐fried chicken. The methods used in this article were intended to achieve maximized fat reduction while maintaining a simple procedure applicable to actual food processing lines.

Transparent, flexible whey protein‐based edible films plasticized with glycerol were produced by wet (solution‐casting) and dry (twin‐screw extrusion followed by compression‐molding) processes. The relationship between the thermal transitions and the heat‐sealability of the whey protein‐based edible films was investigated. Differential Scanning Calorimetry showed the existence of endothermic peaks with an onset transition temperature of 156.3 ± 1.4°C for both the solution‐cast and extruded films. Films were heat‐sealed using an impulse heat‐sealer at an effective jaw pressure of 293.31 kPa, a voltage of 15 V and a cooling time of 4 s. Various impulse times, ranging from 1.5 to 2.5 s, were used to heat‐seal the films. A thermocouple was used to measure the heat‐sealing temperatures at each impulse time. Heat‐sealing temperatures ranged between 126.1 ± 9.0 and 204.0 ± 5.4°C for the shortest and longest impulse times, respectively. Seal strengths were determined using an Instron Universal Testing Machine. Film thickness appeared to have an effect on seal strength; higher strengths were achieved for thinner films, which, in this case, were the solution‐cast films. Thicker (extruded) films required a longer minimum impulse time to achieve a heat‐seal. The highest seal strength (433.07 ± 39.37 N/m) was obtained with solution cast films (thickness of 0.13 ± 0.01 mm) sealed with an impulse time of 2 s (164.6 ± 5.1°C). Impulse times above 2.5 s (204.0 ± 5.4°C) resulted in degradation of both solution‐cast and extruded films. Copyright © 2009 John Wiley & Sons, Ltd.

BACKGROUND: There is a lack of research on producing layered protein–lipid composite films with improved tensile and barrier properties compared to films from individual components. Several film‐forming parameters were hypothesized to influence the extent to which lipids were either dispersed within or layered upon whey protein films. Film‐forming parameters investigated were ratio of whey protein isolate (WPI) to beeswax (BW), homogenization method, sodium chloride (NaCl) concentration, and BW particle size.RESULTS: Film percent elongation (E) increased, while tensile strength (TS) and elastic modulus (EM) decreased when BW was incorporated into WPI films, demonstrating a lubricant effect of the BW. Mean water vapor permeability values for WPI film decreased by 57% when the film composition was modified by the addition of 40% BW. BW phase separation was observed in all of the tested films. Particle size of BW in the film‐forming emulsions was larger in the presence of NaCl (100 mmol L⁻¹), indicating a neutralization of particle charge. However, the addition of NaCl did not improve the moisture barrier of WPI‐BW film over the range of film‐forming conditions used in the study.CONCLUSION: The results from this study are useful in determining formulations and conditions for the production of composite films from WPI and BW with improved tensile and moisture barrier properties. Copyright © 2008 Society of Chemical Industry

ABSTRACT:  The formations of glycerol (Gly)‐plasticized whey protein isolate (WPI)–hydroxypropylmethylcellulose (HPMC) films, blended using different combinations and at different conditions, were investigated. The resulting WPI: Gly‐HPMC films were analyzed for mechanical properties, oxygen permeability (OP), and water solubility. Differences due to HPMC quantity and blend method were determined via SAS software. While WPI: Gly and HPMC films were transparent, blend films were translucent, indicating some degree of immiscibility and/or WPI–HPMC aggregated domains in the blend films. WPI: Gly‐HPMC films were stronger than WPI: Gly films and more flexible and stretchable than HPMC films, with films becoming stiffer, stronger, and less stretchable as the concentration of HPMC increased. However, WPI: Gly‐HPMC blended films maintained the same low OP of WPI: Gly films, significantly lower than the OP of HPMC films. Comparison of mechanical properties and OP of films made by heat‐denaturing WPI before and after blending with HPMC did not indicate any difference in degree of cross‐linking between the methods, while solubility data indicated otherwise. Overall, while adding HPMC to WPI: Gly films had a large effect on the flexibility, strength, stretchability, and water solubility of the film polymeric network, results indicated that HPMC had no effect on OP through the polymer network. WPI–HPMC blend films had a desirable combination of mechanical and oxygen barrier properties, reflecting the combination of hydrogen‐bonding, hydrophobic interactions, and disulfide bond cross‐linking in the blended polymer network.

ABSTRACT:  The effects of glycerol and moisture contents on the thermal transitions of whey protein isolate (WPI) powder–glycerol–water mixtures were studied. Mixtures with ratios of 100:0, 70:30, 60:40, and 50:50 WPI:glycerol on a dry basis (db) were preconditioned to 0.34 ± 0.01 (25.4 ± 0.4 °C) and 0.48 ± 0.02 (25.9 ± 2.2 °C) water activity. Differential scanning calorimetry (DSC) showed the existence of an endothermic peak starting at 148.3 ± 0.7 °C for 100% WPI preconditioned to a water activity of 0.34 ± 0.01. The onset temperature of this peak decreased with addition and increase of glycerol content, as well as with the increase in water activity from 0.34 ± 0.01 to 0.48 ± 0.02. An additional endothermic transition, important for extruding the mixtures into flexible sheets, occurred in mixtures containing 50% glycerol db, preconditioned to 0.48 ± 0.02 water activity. The onset temperature of the peak was 146 ± 2.0 °C. Whey protein‐based sheets containing 45.8%, 48.8%, and 51.9% glycerol db were obtained using a Haake–Leistritz corotating twin‐screw extruder. All samples were obtained at a screw speed of 250 rpm and a final barrel‐temperature profile of 20, 20, 20, 80, 110, and 130 °C. Melt temperature at the time of sheet formation was 143 to 150 °C. Average thickness of the sheets was 1.31 ± 0.02 mm. Samples with 45.8% glycerol db had significantly higher tensile strength (TS) than samples with higher glycerol contents. Also, as glycerol concentration increased, sheet elastic modulus (EM) decreased significantly ( P ≤ 0.05). Extrusion of whey protein‐based sheets is an important step toward extrusion of thinner edible films for food wraps, layers, or pouches.

ABSTRACT:  Increasing interest in high‐quality food products with increased shelf life and reduced environmental impact has encouraged the study and development of edible and/or biodegradable polymer films and coatings. Edible films provide the opportunity to effectively control mass transfer among different components in a food or between the food and its surrounding environment. The diversity of proteins that results from an almost limitless number of side‐chain amino‐acid sequential arrangements allows for a wide range of interactions and chemical reactions to take place as proteins denature and cross‐link during heat processing. Proteins such as wheat gluten, corn zein, soy protein, myofibrillar proteins, and whey proteins have been successfully formed into films using thermoplastic processes such as compression molding and extrusion. Thermoplastic processing can result in a highly efficient manufacturing method with commercial potential for large‐scale production of edible films due to the low moisture levels, high temperatures, and short times used. Addition of water, glycerol, sorbitol, sucrose, and other plasticizers allows the proteins to undergo the glass transition and facilitates deformation and processability without thermal degradation. Target film variables, important in predicting biopackage performance under various conditions, include mechanical, thermal, barrier, and microstructural properties. Comparisons of film properties should be made with care since results depend on parameters such as film‐forming materials, film formulation, fabrication method, operating conditions, testing equipment, and testing conditions. Film applications include their use as wraps, pouches, bags, casings, and sachets to protect foods, reduce waste, and improve package recyclability.